Scale Control Processor Test-Chip
We are investigating vector-thread architectures which provide competitive performance and efficiency across a broad class of application domains. Vector-thread architectures unify data-level, thread-level, and instruction-level parallelism, providing new ways of parallelizing codes that are difficult to vectorize or that incur excessive synchronization costs when multithreaded. To illustrate these ideas we have developed the Scale processor, which is an example of a vector-thread architecture designed for low-power and high-performance embedded systems. The prototype includes a single-issue 32-bit RISC control processor, a vector-thread unit which supports up to 128 virtual processor threads and can execute up to 16 instructions per cycle, and a 32 KB shared primary cache.Since the Scale Vector-Thread Processor is a large and complex design (especially for an academic project), we first designed and fabricated the Scale Test Chip (STC1). STC1 includes a simplified version of the Scale control processor, 8 KB of RAM, a host interface, and a custom clock generator. STC1 helped mitigate the risk involved in fabricating the full Scale chip in several ways. First, we were able to establish and test our CAD toolflow. Our toolflow included several custom tools which had not previously been used in any tapeouts. Second, we were able to better characterize our target package and process. For example, STC1 enabled us to better correlate the static timing numbers from our CAD tools with actual silicon and also to characterize the expected rise/fall times of our external signal pins. Finally, STC1 allowed us to test our custom clock generator. We used our experiences with STC1 to help us implement the Scale vector-thread processor. Scale was taped out on October 15, 2006 and it is currently being fabricated through MOSIS. This report discusses the fabrication of STC1 and presents power and performance results.